It depends on how many of these things they are doing. If they're only tackling the story in one movie, it'll probably stumble. Not so much because because of any Americanizing, but more because it's really difficult to adapt all that hijinks into one feature. Even the Japanese ones split everything into two movies and changed a lot of stuff around. Had they not gone with the ending they used, they would have needed even more direct sequels to adapt the parts they didn't do too. I doubt there will be any internal monologuing in this one, and that could make things even more difficult since almost everything is exposited through people's thoughts in this bloody series.

Spoiler:

On the plus side, even if it does suck, at least L will still sit like a complete dillhole.

If the whole potato chip scene is reenacted with as much fervour as in the anime, then the whole venture was worth it.